Flex bay support:Up to two half-height optical drives, or;Up to two 5.25” slim ODD cages, or;Up to two 5.25" slim ODD and HDD cages, or;Up to one Front Access Storage Enclosure, or;Up to one flex module for one or more of the following options: 9.0mm optical/15-in-1 USB 3.0 reader/front eSATA/front Thunderbolt/4-digit diagnostic displayNOTE: Only one can be supported from 15-in-1 reader, Thunderbolt, and 4-digit display.